If you do something like "netstat -leanp | grep 80" you should see whether Apache is listening on that port or not. However, the firewall may still be blocking that port; check your iptables configuration to make sure.
I usually use "lsof -i -n" (list open files, IP ports only, numeric (no DNS lookups)), but one must be root to use this. As with netstat, pipe the result through grep to identify specific ports.
